Ground source heat pumps are known for use in controlling temperatures in buildings and other structures. A typical ground source heat pump comprises an outdoor coil for transferring heat from or to the ground, an indoor coil for transferring heat from or to the environment sought to be controlled, and a compressor compressing a refrigerant, and thereby adding heat to the refrigerant, and discharging the refrigerant to either the outdoor coil or the indoor coil, depending upon the mode in which the heat pump is operating.
A number of problems have been presented by known heat pump designs. A typical heat pump utilizes a piston or reciprocating compressor which must be activated under equalized pressure conditions and gradually build up to the high pressure operating conditions of the condenser coil circuit. Thus, once the desired temperature has been reached in the indoor environment and the compressor is deactivated, the high pressure refrigerant in the condenser circuit must be permitted to equalize with the low pressure refrigerant in the evaporator circuit to enable the compressor to restart when the temperature of the controlled environment changes. This reduces efficiency of the heat pump by requiring the compressor to build up condenser circuit pressures after each startup. This further requires that the compressor remain off after deactivation for sufficient time to allow pressure equalization to occur.
A greater amount of refrigerant is required in the cooling mode than in the heating mode. In a typical heat pump the refrigerant charge must be increased manually when switch-over to the cooling mode becomes necessary. Insufficient refrigerant charge in the cooling mode reduces the efficiency of the heat pump.
Heat pumps are subject to "slugging" when the level of refrigerant exceeds an optimum level, so that the proportion of liquid refrigerant to gaseous refrigerant becomes too high resulting in overfeeding the accumulator. This can damage the compressor.
The present invention overcomes all of these disadvantages. The present invention utilizes a scroll compressor having a pressure dome with a check valve on the compressor discharge port which operates in conjunction with a solenoid valve to trap high pressure refrigerant in the condenser circuit and low pressure refrigerant in the evaporator circuit during off cycles. This improves the efficiency of the heat pump by obviating the need to rebuild condenser circuit pressure after each start-up, or to wait for pressure equalization between the condenser circuit and the evaporator circuit prior to restarting the compressor.
A solenoid valve controlled by suction pressure and accumulator refrigerant level is provided upstream of the evaporator (indoor coil) in cooling mode to facilitate the flow of refrigerant and alleviate a low suction pressure condition upon start-up.
A charge control device acts as a reservoir for excess refrigerant in the heating mode and automatically delivers refrigerant to the evaporator circuit in the cooling mode to increase the refrigerant charge as required to maximize efficiency.
To avoid "slugging" an accumulator is provided with a reed switch to control the level of refrigerant in the accumulator, and thus avoid a dangerously high proportion of liquid refrigerant to gaseous refrigerant circulating through the compressor. Further, a heat exchanger is provided whereby prior to compression cool refrigerant absorbs heat from warm refrigerant, thus decreasing the ratio of liquid refrigerant to gaseous refrigerant entering the accumulator.